LED Display - The LED
display is simple. It is setup to flash the lights serially. This was done so
when the car is armed, it would look similar to the display in front of the car
“Kit” in the show “Knight Rider”. The LED’s are connected to a header,
which is connected to the receiver board via a ribbon cable.
Figure 2: LED Display
Transmitter - The transmitter is required to send three different signals: arm, disable, and panic. We decided the best way to do this was to make the PIC send out different codes, depending on which pin had a transition from HIGH to LOW. The way we did the transition was to have the pin sitting high, by use of a pull up resistor. But when a button is pressed, the pull up resistor is bypassed and the pin on the PIC goes straight to ground. There are three buttons that do this for the three different signals that need to be sent. The signal is sent to the receiver board via an AM-RT5-418 transmitter. The antenna use is a 16.5 cm whip antenna.
Figure 3: Transmitter Circuit
Car Circuit - Instead of installing the car alarm into a car, we decided to simulate the car by using a circuit. This circuit has 12 volts coming in from the battery. The 12 volts is also connected to the receiver circuit via a header and ribbon cable. There are two toggle switches that switch between ground and 12 volts. These switches are used to simulate the driver side and passenger doors. All inputs from the car are 12 volts. When the car door is closed the wire that we are using to trigger the alarm on is sitting at 12 volts. When the car door is opened, the wire will be shorted to ground. This is the condition that we are using to trigger the alarm. The condition that the car is armed is explained in the receiver section. There are two relays that need to be installed in the car. These relays are used to disconnect/connect the ignition from/to the starter and also turn on/off the hazard lights. The relays are driven using a PNP-NPN configuration. This is done because during power up, the microprocessor outputs are pulled high, so driving the relays with a PNP-NPN configuration keeps them from momentarily firing.
Figure 4: Car Circuit
Receiver Circuit - There is a voltage regulator that converts the 12 volts to 5 volts, which powers the PIC. The inputs from the car are 12 volts, so the only thing needed to interface them with the microcontroller is to adjust them to 5 volts. Two 1N4004 diodes are used to block the incoming the 12 volts. The 1N4004 diodes, rated at 400 PIV, were used because spikes in an automobile electrical system can get quite large. The microcontroller pins are then pulled HIGH using pull up resistors. An AND gate is used to AND the two inputs from the car. This is so if either of the car doors is opened, there will be a transition from HIGH to LOW, on the microcontroller pin, and the alarm will be triggered. A PNP-NPN configuration is used to drive the horn in the car. The output of this configuration is connected to the car circuit via a header and ribbon cable. The PIC is connected to the display circuit via a header and ribbon cable. The PIC receives the data from the AM-HRR3-418 receiver.
Figure 5: Receiver Circuit